It is well known to produce xylylenediamine from xylene by the ammoxidation of xylene into dicyanobenzene and the subsequent hydrogenation of the resultant dicyanobenzene into xylylenediamine in the presence of a catalyst.
Non-Patent Document 1 discloses a method of producing xylylenediamine from xylene, in which xylene is ammoxidized into dicyanobenzene and the separated dicyanobenzene is hydrogenated into xylylenediamine in the presence of a catalyst. However, this document is quite silent about the details of the process such as the extraction of dicyanobenzene from the gas produced by the ammoxidation.
Patent Document 1 discloses a method of producing m-xylylenediamine from m-xylene. In the proposed method, isophthalonitrile produced by the ammoxidation of m-xylene is extracted into an organic solvent. Then, high-boiling point impurities are separated out in the first distillation step and the organic solvent is separated out in the second distillation step. Then, isophthalonitrile is taken out of the bottom of apparatus. The obtained purified isophthalonitrile is then hydrogenated after the addition of a specific solvent and liquid ammonia. This method requires increased costs for constructing production facilities because of its large number of steps. In addition, the method requires two distillation steps before the hydrogenation and further requires another distillation step for purification after the hydrogenation step. Therefore, a great quantity of energy for distillation should be consumed.
In the method disclosed in JP 2002-105035A, the ammoxidation gas containing dicyanobenzene from the ammoxidation of xylene is directly contacted with an organic solvent to extract dicyanobenzene into the organic solvent. The extracted dicyanobenzene is added with liquid ammonia and then hydrogenated without separation. Since the organic solvent for extracting dicyanobenzene from the ammoxidation gas should be stable under the hydrogenation conditions, the kind of organic solvent usable in this method is limited. Methylbenzonitrile, which is by-produced in the ammoxidation of xylene, is a suitable solvent for extracting dicyanobenzene from the ammoxidation gas because of its high dissolving power to dicyanobenzene. However, since the nitrile group of methylbenzonitrile is hydrogenated under the hydrogenation conditions, methylbenzonitrile cannot be effectively used as the solvent for extracting dicyanobenzene in the method of Patent Document 2 in which the solvent containing the extracted dicyanobenzene is directly fed into the hydrogenation step. Since methylbenzonitrile is an intermediate of the production of dicyanobenzene, methylbenzonitrile can be converted into dicyanobenzene if it can be recovered by separation and reused in the ammoxidation. However, the recovery of methylbenzonitrile is impossible in the proposed method for the reason mentioned above. In addition, xylylenediamine produced by this method usually contains a large amount of impurities, and therefore, may cause problems when used in applications requiring high purity, such as the production of high quality polyamide.
In the method of producing xylylenediamine disclosed in Patent Document 3, the ammoxidation gas from the ammoxidation of xylene is directly contacted with an organic solvent to extract dicyanobenzene in the ammoxidation gas into the organic solvent. The organic solvent containing the extracted dicyanobenzene is added with liquid ammonia and then dicyanobenzene is hydrogenated without separation. After the extraction using a specific solvent and water, xylylenediamine is finally purified by distillation. In this method, the kind of usable organic solvent is also limited because the organic solvent is required to be stable under the hydrogenation conditions. In addition, both the extraction and distillation are required to obtain a highly pure xylylenediamine, this making the process complicated and increasing the costs of constructing production facilities. Further, the distillation of the liquid mixture of xylylenediamine and water obtained by the water-extraction needs a great energy consumption, because a large amount of water having a large evaporation latent heat should be distilled away.
Patent Document 1: JP 2003-26639A
Patent Document 2: JP 2002-105035A
Patent Document 3: JP 2003-26638A
Non-Patent Document 1: Process Handbook (1978) edited by The Japan Petroleum Institute